Zack turns 23 in a month. You won't get a better idea about his future until next season when he turns 24. If he is still having the same problems and isn't getting any better towards the end of next season then he is a bust/disappointment. You'll have a much better idea about Kassian by the end of next season. For right now disappointment is a bit of a strong word.
For those comparing him to Hodgson, look at it this way: Hodgson is improving on his defensive skills, you can definitely see the improvement from last season but at most his defense at its best will be average. The one thing that he will always lack is speed and that is one thing that will follow him throughout his career. The most he can do to improve a little in that regard is work on his technique with the Sabre's skating coach.
Kass has the tools to excel. He's big, fast, and on occasion shows that he can score goals. I've said it before, what will make him or break him is his coaching. If in the end he can be molded into a second line staple then he will have been well worth the price. Right now Hodgson is only on the Sabre's first line by default, but on any good team he would be a second liner and there's nothing wrong with that.
For now, just expect Kass to be a very average third liner. At this point in his career, that's not a bad thing. If he's still only very average or worse towards the end of next season though, that would be the time to panic and complain.